The effect of variations in temporal bone structure upon the caloric response.

A high degree of inter-subject variability reduces the clinical usefulness of the caloric test. Both anatomical and physiological factors are responsible for this problem, but the proportion of variability caused by either factor has not been determined. This study sets a quantitative estimate on the amount of caloric test variability which can be ascribed to anatomical variations in the study population. Polytome radiographs of 48 "normal' subjects were studied do determine how individual variations in the intensity of caloric-induced nystagmus might be related to anatomical features of the temporal bone. A statistical analysis showed that pneumatization in the petrous and "buttress' areas, and the dimensions of the internal auditory canal were significantly correlated with caloric response intensity. Furthermore, about 23% of caloric response variability in this population could be accounted for by a combination of anatomical characteristics. However, neither the extent of mastoid pneumatization nor the dimensions of the external auditory canal were found to be significantly related to caloric responsiveness.